This invention relates to geochemical prospecting and exploration for subsurface deposits and more particularly to apparatus for detecting subsurface accumulations of hydrocarbon deposits, geothermal reservoirs, uranium or other mineral deposits by means of analysis of subsurface interstitial gas samples. Still more particularly, this invention relates to an apparatus for collecting gas samples and obtaining other important soil parameters which are useful in analysis of the gas samples.
Known subsurface gas sampling techniques are based upon the well known fact that geochemical and geophysical forces act upon subsurface accumulations of hydrocarbons or minerals and cause migration of many of the elements and compounds into the surrounding soil strata. Decomposition may take place during migration, resulting in primary and secondary constituents being partially or completely absorbed into surrounding soil or rock.
Typically, the concentration of such constituent elements is greatest at the surface above the source, and thus, analysis of concentration data concerning specific constituent elements can result in valuable information concerning the location of hydrocarbon deposits, geothermal reservoirs or mineral ore deposits. The development of concentration patterns is affected by many parameters, including: temperature, moisture, partial pressures, porosity of the soil strata and others.
Previously known apparatus for sampling subsurface gas have included simple mechanical probes and various bore hole techniques. One such example is depicted in U.S. Pat. No. 3,490,288, issued to H. W. Patnode. U.S. Pat. No. 3,490,288 is a mechanical probe which utilizes a rubber septum in the point to prevent contamination of the sampling passage, prior to sample selection. Such systems encountered great difficulty in preventing contamination, as the rubber septum at the point was often subject to damage during the driving of the probe into the soil.
An attempt to solve the problem encountered by contamination entering the sampling passage prior to sample selection is illustrated in U.S. Pat. No. 3,835,710, issued to L. A. Pogorski. U.S. Pat. No. 3,835,710 depicts a mechanical probe with a chisel shaped point assembly. The sample passage is a point at or near the threaded portion of the shaft which is received into the point assembly. At the appropriate sampling depth, the shaft is rotated to expose the sample passage. Difficulties have been encountered with this type of apparatus due to the chisel shaped point assembly rotating with the shaft.